2018.06.30
Professor Oak has discovered that Pokémon can become even stronger by Mega Evolving. Not much is known about this type of evolution. However, we do know that you need a Key Stone to trigger it.

If you can put the pieces together, you may be able to help Professor Oak with his research and obtain the Key Stone!

_______________________________________________________

2018.07.04
Professor Oak, with the help of Roark, have discovered how to make Pokémon mega evolve. There are a couple things you need to complete on your quest for Megas. First, you need to have put the pieces together and found the Key Stone. Next, you will need to talk to Roark and see if he thinks you are a worthy enough trainer to receive some of the special items he has discovered. If you can prove your worth, you may receive something truly mega!

Mewtwo is currently available as a prize via the Click Exchange. If you are lucky enough to find it, it will have the 2nd promo star.

To do the math, there are 48 total Mega Evolutions. Virtuadopt has already seen Mega Groudon and Mega Kyogre as special promos. Counting Mega Charizard X and Mega Charizard Y as confirmed in some fashion, likely a forme change for existing adopts, that leaves 44 Mega Evolutions with unknown status on this site.

And also Meloetta Pirouette Forme, which has existing art, and the other two formes of Zygarde; 10% and 100%, which do not.
And Therian Thundurus, Therian Tornadus, and Therian Landorus, which also do not have existing art.

Well, since it says "Keep your eyes on https://www.virtuadopt.com/ for further updates #soon." on yankees post I don't think they're obtainable yet...
I'm sure we'll learn more about how to get them once they're released

Well now. This is getting more interesting. I figured it was going to be a generic Mega Stone and X and Y variants for Charizard and Mewtwo. This would indicate a little bit of effort in the coding department.